1. Field of the Invention
The present invention relates generally to a paper feeding device including a bottom plate lifting mechanism without motor and an image forming apparatus including the paper feeding device.
2. Description of the Related Art
In a paper feeding device used for an image forming apparatus, when paper sheets are taken and fed one by one from a bundle of paper sheets stacked and placed on a bottom plate in a paper housing unit, it is necessary to press the bundle of paper sheets against a paper feeding roller that is provided above the paper sheets prior to paper feeding. For this reason, in general, a mechanism that lifts the bottom plate is provided in a sheet housing unit. A spring pressure system and a motor control system are known for bottom plate lifting systems using the mechanism that lifts the bottom plate.
In general, in the spring pressure system, a spring is stretched by manual attachment of a paper feeding tray, or a spring that is compressed in advance is released, to push up the bottom plate. The motor control system lifts the bottom plate by a motor force.
The conventional spring pressure system is mechanically simple and inexpensive but has a disadvantage that the force of attaching or detaching the paper feeding tray is heavy and thus the operability lowers, so that the user has to push down the bottom plate. In short, while the conventional spring pressure system achieves cost reduction because mechanoelectrical parts are not used to lift the bottom plate, the bottom plate cannot be lowered automatically. For this reason, the user has to push down the bottom plate manually.
On the other hand, because the motor control system is for lifting the bottom plate by motor force, the disadvantage of the spring pressure system described above is significantly recovered. However, there is a problem that the motor requires mechanoelectrical parts, such as an inversion prevention mechanism, a paper upper limit detection sensor, and a lift lever lower limit detection sensor, which increases the costs.
For the purpose of reducing the costs of a structure of a device that lifts a bottom plate, Japanese Laid-open Patent Publication No. 2011-131960 discloses a structure for transmitting a rotation force obtained from, for example, a main motor instead of a drive motor, such as a lifting motor, to a toothed gear to drive the toothed gear and for lifting a bottom plate by using a flapper solenoid. However, because mechanoelectrical parts are necessary, that is, mechanoelectrical parts cannot be excluded, the problem of cost increase cannot be solved.
Therefore, there is a need to provide a paper feeding device including a bottom plate lifting mechanism that enables cost reduction by excluding mechanoelectrical parts but without lowering the tray operability, and an image forming apparatus including the paper feeding device.